Battle of the Zab

Beside the Great Zab, a tributary of the Tigris in northern Iraq, the army of the last Umayyad caliph, Marwan II, was routed by Abbasid forces on 25 January 750. The defeat destroyed the military power of the Umayyad Caliphate, and confirmed the triumph of the Abbasid Revolution. The Abbasid Caliphate that replaced it would endure until 1258.

By the 740s the Umayyad state was badly weakened. A disputed succession in 744 set off a civil war, the Third Fitna, followed by a Kharijite rising and other revolts. Marwan II, who took power in 744, spent his first years fighting rival Umayyads and rebels, and moved the capital from Damascus to Harran in upper Mesopotamia, a decision that provoked a further rebellion.

Meanwhile a clandestine movement, the Hashimiyya, had for years been seeking support in Khurasan, in the north-east, for a ruler from the family of the Prophet. The Abbasids, descendants of Muhammad's uncle al-Abbas, used memories of the Battle of Karbala to rally opposition. In June 747 their agent Abu Muslim raised the black banners near Merv. Abbasid armies under Qahtaba ibn Shabib swept westward across Iran, defeating several Umayyad forces, and by August 749 reached the Euphrates near Kufa. Ibrahim al-Imam, head of the Abbasid family, was seized on Marwan's orders and died in captivity, but his brother Abu al-Abbas, later known as al-Saffah, was recognised as caliph in the mosque at Kufa on 28 November 749.

With southern Iraq in Abbasid hands, Marwan marched from Harran with a large army of Syrian troops and based himself at Mosul. An Abbasid force advanced up the Tigris, and al-Saffah placed it under the overall command of his uncle, Abd Allah ibn Ali. Figures in the sources vary greatly; one estimate gives the Abbasids 10,000 to 30,000 men and the Umayyads 100,000 to 150,000, but such numbers are uncertain. From mid-January the two sides skirmished for several days, with small successes on each side.

On 25 January Marwan led his men across a bridge of boats to attack. His army, though larger, was divided by tribal rivalries, and the fight began prematurely when one Umayyad commander charged the Abbasid right without orders. The Abbasid horsemen dismounted and knelt in a tight line with spears levelled, while archers behind them shot at the advancing cavalry, and the Syrian charges broke against this wall.

As the Umayyad line began to give way, Marwan is said to have tried to rally his troops by offering money, which only caused disorder as soldiers fought over it. Other units took the confusion for a retreat and fled towards the river. When the bridge was cut to stop the pursuit, many of Marwan's own men were trapped and drowned.

Marwan escaped and fled through Syria and Palestine to Egypt. An Abbasid detachment followed him and he was killed at Abusir, in the Nile Delta, on 6 August 750. His death was followed by a ruthless hunt for the rest of the Umayyad family. Abd Allah ibn Ali offered an amnesty, and about eighty Umayyads who gathered to receive it were massacred. Umayyad tombs in Syria were desecrated, except that of the caliph Umar ibn Abd al-Aziz.

One prince, Abd al-Rahman, a grandson of the caliph Hisham, escaped to Spain, where he founded an Umayyad state at Córdoba that lasted until 1031. Elsewhere the Umayyad cause was finished, and the Abbasids held the caliphate's heartlands.

Our 700 map shows the Umayyad Caliphate at the height of its expansion, and the 800 map shows the Abbasid Caliphate in its place, with the Umayyads surviving only in Spain.